The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
Power sources, chargers and other units connected to main supplies are sometimes equipped with a light-emitting diode (LED) for indicating when the device is connected to a mains outlet and powered. A lit indicator encourages the user to switch the apparatus off or disconnect it from the mains outlet when not in use.
However, a LED is consuming standby energy if the user leaves the device on continuously. If the power for the LED is taken from the power source output, the power consumption is not negligible. A LED needs only few milliwatts for its operation, but power supply efficiency is extremely low with a small load. Thus, a LED may take several times the nominal power from the mains supply. If the LED is placed in the primary side of the power source or charger, the energy loss is still not negligible as a regulator is needed to provide the LED with a constant current. In solutions designed for low standby power, an X-capacitor supply is commonly used. However, especially on multivoltage power supplies the LED power stabilization is not power-efficient.